Mapping Video BIOS?

Bruce M Simpson bms at
Sat Jul 26 01:43:39 PDT 2003

On Sat, Jul 26, 2003 at 05:32:17PM +0930, Greg 'groggy' Lehey wrote:
> Can anybody point me in the right direction?  Where should I be
> looking for this?  Is this memory mapped permanently, or is it only
> during X startup?

The video BIOS is usually mapped by system BIOS into real memory to
begin with, so it should be just sitting there.  There are usually northbridge
chipset registers for dealing with this sort of thing.

The SMM mode might reuse that window, though, but generally this is hidden
from non-SMM mode applications.

You're in luck - been rebuilding X, so have xc tarballs handy.

The XFree86 code responsible is: xc/programs/Xserver/hw/xfree86/int10
Some drivers like to call VBE via int10h, so this module acts as a bridge.
It just memcpy()'s the ROM and uses various methods, depending on the
compilation target, to call int10h.

Is the onboard video AGP/PCI? It is possible that the device isn't reporting
its memory window in the ROM BAR correctly. I've seen this happen with some
low-end network cards before.

Try my tools at this URL to check this:


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